1. Field of the Invention
The present invention relates to an apparatus and a method for generating a phase-locked signal by extracting a copy guard signal from a display signal, and, more particularly, to an apparatus and a method of generating a video-reproducing clock signal from a 480p signal, in which a coast signal is generated in accordance with a change in the format of the copy guard signal.
2. Description of the Related Art
Video signals can be transmitted, received, processed, and displayed in the format of progressive scanning or interlaced scanning. In progressive scanning, also referred to as non-interlaced scanning, video images are displayed as a consecutive frame. All horizontal lines in each frame are displayed in consecutive order. In a standard image format, i.e., a 480p format, all 480 horizontal lines (in sequence from 1-480) in a frame are displayed in consecutive order.
FIG. 1 illustrates a typical 480p-format composite video signal. The 480p-format composite video signal of FIG. 1 includes a vertical synchronization signal (V_sync) 101, horizontal synchronization signals (H_sync) 102, and copy guard signals 103. The vertical synchronization signal 101 is generated at the beginning of frame 100. The horizontal synchronization signals 102 are generated when a new horizontal line starts. The copy guard signals 103 are intended to prevent copying of video signals in question. The copy guard signal 103 is inserted between two respective horizontal synchronization signals 102 in a 4×9 format (which is, 4 pulsed signals for each of 9 horizontal synchronization signals) just after the vertical synchronization signal 101 has been generated.
A scaler, which converts the format of RGB video signals to match the resolution of a display in question, and an analog-to-digital converter (ADC), which converts an analog signal to a digital signal, operate in response to a phase-locked clock signal generated by using the horizontal synchronization signals 102. In a conventional approach for extracting only the horizontal synchronization signals 102 from the 480p-format composite video signal of FIG. 1, a window signal, called a coast signal, is generated in a component of the ADC or scaler to cover an area, which includes the copy guard signals 103. While the coast signal is being generated instead of the original horizontal synchronization signals 102, artificial horizontal synchronization signals are generated with a regular period and input to the phase-locked loop (PLL). In this way, it is possible to prevent the occurrence of undesired clock signals due to the copy guard signals 103.
However, if the format of the original video signal changes and the format of the copy guard signal 103 changes, it is impossible to generate an adaptive clock signal in accordance with the changes, because the coast signal may have a fixed length for 4×9 format of copy guard signals 103.